The deadline is 31 January 2019 to get returns in before financial penalties are issued.
An initial £100 fine is given for late returns, and after three months, £10 a day is charged up to £900.
HM Revenue and Customers (HMRC) expects more than 11.4 tax returns to come in, but only around half had been submitted by the end of December.
Anyone who earned more than £2,500 from renting out property and self-employed sole traders are among those who need to complete a return.
Mortgage tax relief changes take place
It’s thought many landlords filling out their tax returns this year will start to realise the effect of new mortgage relief tax rules which are currently being phased in.
In the tax year 2017 to 2018, only 75% of finance costs – such as mortgage interest – can be deducted from income, and the remaining 25% is available as a basic rate tax reduction.
By 2020 to 2021, all finance costs will be limited to the basic tax rate reduction.
Angela MacDonald, HMRC’s director general for customer services, said: “The self assessment deadline on 31 January is fast approaching, but there is still time for customers to file their tax returns online and on time to avoid any unnecessary penalties.
“If you are completing self assessment for the first time or are yet to start your 2017 to 2018 tax return, there is a wide range of support and guidance available on GOV.UK to help at every stage of the tax return process.”
People who completed a tax return last year but didn’t have any tax to pay still need to complete a 2017 to 2018 tax return unless HMRC has written to them to say it is not required.
